DESCRIPTION: Otitis media (middle ear infection) ranks first among the most common diagnoses requiring a physician's office visit and recent estimates indicate that virtually all children (99%) will experience at least one episode of otitis media (OM) by age 2. The disease progresses in many children to recurrent infections and chronic inflammation, often with complications and sequelae that include persistent hearing loss and communication disorders. The socioeconomic impact of this disease is significant. Approximately four billion dollars are spent annually on treatment of OM. Nontypeable strains of Haemophilus influenzae (NTHi) are significant OM pathogens and account for 25- 30% of all cases of OM, 53% of recurrent OM, and are the primary pathogens isolated from 62% of cases of otitis media with effusion. The virulence factors and protective antigens of NTHi have not been completely defined and a vaccine is not available. Collective data from this and other laboratories indicate that endotoxin, or its subcomponent lipooligosaccharide, both an integral component of the outer membrane of gram negative bacteria and potent inflammatory mediators, are refractile and present in a large percentage of middle ear effusions. Therefore, it is important to continue to define this macromolecule's role in OM and toward this end the specific aims of this proposal are: 1) To assess NTHi lipooligosaccharide (LOS) as a virulence determinant for nasopharyngeal colonization and the induction of otitis media using NTHi gene-disrupted mutants with altered LOS phenotypes; 2) To determine the relationship of NTHi LOS phase variation to OM pathogenesis; 3) To assess the role of endotoxin/LOS-induced TNF alpha in the pathogenesis of OM; 4) To expand our preliminary data which suggests that endotoxin binds selectively to middle ear goblet cells and other structures in the middle and inner ear in order to begin to evaluate endotoxin receptor-function in the pathogenesis of OM. All these aims are focused to achieve our long term goal which is to define the role of endotoxin in the pathogenesis of OM so that we can ultimately design better prevention and treatment modalities.